Dental caries (demineralization, decay) ranks among the most significant of human diseases simply because of its frequency of occurrence in the modern world where over 90% of the population is affected, ranking dental caries first amongst the chronic diseases affecting humans in terms of the numbers of people involved. (see Poole, D. F. G. and Silverstone, L. M. in Hard Tissue Growth, Repair and Remineralisation pp 35–52 Ciba Foundation Symposium No. 11, Elsevier Scientific Publishing Company, 1973; Legler D. W. and Menaker, L. in The Biological Basis of Dental Caries; Menaker, L. pp 211–225, Harper & Row, 1980; Winston, A. E. and Bhaskar S. N. JADA 129:1579–1587, 1998, Achievements in (US) Public Health, 48(41):933, 1999).
Although the severity of this disease in terms of its life threatening potential is limited to rare instances, certain important consequences exist. Dental caries treatment is costly (requiring highly skilled and exacting manpower as well as complex biomaterials), it is time consuming, it often involves pain and discomfort (both because of sequellae and treatment); it affects aesthetics and furthermore there is a need to avoid or limit restorative dentistry because of the potential hazards of radiation, treatment and dental materials slowly degrading in the oral cavity over many years (see Nathanson, D. et al. JADA 128:1517–1523, 1997; Berry, T. C. et al. JADA 129:1547–1556,1998; Saxe, S. R. et al. JADA 130:191–199, 1999; Soderholm, K. J. and Marlott, A. JADA 130:201–209, 1999).
The major etiological factors involved in the demineralization process (dental caries) is the interplay over time of host factors (the teeth and the saliva), the microflora and the diet. Many factors can prevent dental caries such as oral hygiene, diet, fissure sealants and fluoride; the latter being the most simple, least time consuming and the most cost effective. Indeed, teeth are not dead tissue as they undergo ion exchange which determines whether there is demineralization or remineralization. The demineralization leaves the soft tooth matter porous but it has been shown that within certain limits tooth tissue may recover its original hardness after remineralization. In all cases remineralization processes are significantly enhanced by the presence of fluoride ions (Poole, D. F. G., Silverstone, L. M. in Hard Tissue Growth, Repair and Remineralisation, pp 35–52 Ciba Foundation, 1973; Donty, K. J. et al. JADA 130:817–825, 1999) for adequate periods of time or frequency (Ostrom C. A. in the Biological Basis of Dental Caries, Menaker L. 445–460, Harper & Row, 1980).
Tooth mineral consists primarily of carbonated calcium hydroxyapatite (substitutions of carbonate for a portion of phosphate in calcium hydroxyapatite) which becomes increasingly soluble as the localized pH drops. Teeth are in a constant flux of demineralization when the pH drops and remineralization when the plaque acids are neutralized by the saliva. Remineralization occurs when calcium and phosphate ions are present in adequate proportions forming hydroxyapatite which is less soluble than original carbonated calcium hydroxyapatite. However, when fluoride is present fluorapatite is formed which is even less soluble than hydroxyapatite and remineralization of carious lesions occurs when fluoride also allows the deposition of a mixture of fluoride salts. Furthermore, fluoride has antimicrobial activity itself (Ostrom, C. A. in the Biological Basis of Dental Caries, Menaker, L. 445–460, Harper & Row 1980; Kautsky, M. B. and Featherstone, J. D. B. Caries Res. 27, 373–377, 1993).
The disadvantage of current topical fluoride applications are toxicity, dilution and buffering effects of saliva, the lack of ability to reach into all susceptible sites, especially interproximally (Guo M. K. et al. J. Dent. Res. 68:496–498, 1989) and failure to penetrate through the depth of plaque and the need for relatively frequent applications. These failures are primarily governed by the lack of time that the topical fluoride can be held in the mouth and by the potential toxicity of swallowing the active agent which is used in a gross form and in relatively large amounts, even by more advanced methods (U.S. Pat. No. 5,770,182) which is also cumbersome, uncomfortable, unhygienic and fails to reach contact points or areas of teeth. An attempt to overcome some of these problems was reported by Rose K. et al J. Dent. Res. IADR Abs. 77:972, 1998. It is felt that the wedges described therein would not physically reach the contact points or areas of teeth and they would not be retained for extensive periods in a clinical situation because of physical and chemical considerations. Another approach is U.S. Pat. No. 6,136,297 which also does not deal with directly negotiating the contact points or areas, nor does an extensive literature review (Rawls, H. R. Adv. Dent. Res. 5,50–55 1991) refer to this approach. Furthermore, nor do orthodontic bands, which hold archwires onto orthodontic brackets, and release fluoride (available in the U.S.A. from Ortho-Byte) specifically target the interproximal contact points/areas. Rather, these bands release the fluoride into the saliva.
Referring to FIG. 1, there are primarily three tooth zones that are more susceptible to caries:—the fissures, marked (A), the contact points/areas (B1) (approximal zones) of interproximal regions marked (B), and the cervical margins, marked (C), which can extend into the interproximal sites at the gingival margins. Contact points exists between adjacent teeth: with aging, these points wear to form small areas of contact. Fissure sealants are reasonably effective for fissures but besides being costly and not always durable, they are not applicable to interproximal regions which are even more costly and difficult to treat. Topical fluoride applications (e.g., as in U.S. Pat. Nos. 5,770,182 and 6,136,297) are effective at cervical regions which are more prevalent today as geriatric patients have saved many of their teeth with exposed weaker dentin due to gingival recession (Mandel, ID Quintessence Int. 16,81–87 1985). However, there is a need for a more localized or targeted means of preventing microscopic cervical caries.
Dentinal caries comprises four zones, namely the infected necrotic zone, the infected superficial demineralized zone, the affected deep demineralized zone and the hypermineralized zone (Massler, M. Dental Clinics of North America pp 663–673, 1967). Although bacteria are abundant in the superficial demineralized zone only on rare occasions are a few bacteria found in the affected deep demineralized zone which comprises well formed residual tubular matrices. Indeed the major difference between this zone and sound dentin appears to be depletion of the mineral components. The clinical appearance at this zone is that of dry leathery dentinal structure (Hoffman, S. in The Biological Basis of Dental Caries. Menaker, L. pp 226–246, Harper & Row, 1980) which is the dentin collagen which may be partially denatured. Current dental treatment involves mechanically removing this layer and the more superficial layers using drills and mechanical excavation. Attempts to avoid this invasive and painful technique include air abrasion, lasers, atraumatic restorative therapy, and chemomechanical caries removal. None of these techniques have been fully accepted clinically because of a series of disadvantages and failures. This further emphasizes the need for effective preventative techniques.
An aim of the present invention is to provide a system for the controlled or sustained delivery of a material having a desired or predetermined activity to a desired dental site in the oral cavity that overcomes the disadvantages of prior art systems.
It is another aim of the present invention to provide such a system that is particularly directed to the contact points/areas of interproximal sites.
It is another aim of the present invention to provide such a system that employs a matrix as a carrier for the active material.
It is another aim of the present invention to provide such a system in which the matrix for the active material may be biodegradable, resorbable or non-resorbable.
It is another aim of the present invention to provide such a system which is particularly adapted for physical fixation onto the dental site, in particular on and/or around the interproximal contact points/areas, for at least a predetermined time period, typically sufficient to enable the controlled or sustained delivery of a required quantity of the active material from the matrix to the site.
It is another aim of the present invention to provide such a system in which fixation of the matrix is by way of a physical property of the matrix, in particular wherein the matrix comprises a hydrophilic polymer which softens and swells in situ by the hydration thereof in the oral cavity after accommodation at the dental site.
It is another aim of the present invention to provide such a system in which physical fixation of the matrix is primarily by means of a carrier member which is itself adapted on the one hand to accommodate the matrix and align the same with the dental site, and on the other hand is also adapted for affixing the carrier at the site by virtue of its shape, configuration and elasticity/resilience of the material from which it is made. In particular, such adaptation includes sufficient elasticity and toughness of the matrix material, which are important criteria when positioning the matrix between teeth.
It is another aim to provide such a system wherein the matrix is sufficiently flexible for insertion into the interproximal site, and at the same time of sufficient toughness to maintain mechanical integrity thereat, while being soft enough not to be a source of discomfort within the oral cavity.
It is another aim of the present invention to provide any one or combination of a plurality of chemical and other agents that have a desired activity at the dental site, in particular such as to enable inter alia the prevention, treatment, diagnosis, elimination or retardation of dental caries at tooth surfaces or at tooth interfaces with restorations or prostheses.
Other purposes and advantages of the invention will appear as the description proceeds.